Heat the oven to 180 degrees.
Mix together the flour, baking powder, cocoa and salt.
Whip the egg yolks with the sugar (140 g) for about 5 minutes (the mixture must become very light yellow).
Beat the egg whites and add the cream of tartar; whisk until they become frothy. Slow down the speed and add the remaining sugar (30 g).
Increase the speed and continue to whisk for another 5 minutes, until you have a firm meringue.
Add a part of the egg whites to the yolks mixture, mix well from bottom to top and, once the compounds are well assembled, add the remaining egg whites.
Pour the mixture into the pan without flour or butter it. Bake at 170 ° for about 40 minutes (do the toothpick test to check cooking).
Remove from the oven and turn the mold upside down until completely cooled. Finally remove the removable bottom of the mold and place the cake on a wire rack.
When the cake is completely cooled, decorate it with the Nutella in spoonfuls, distributing it evenly over the whole cake and leveling it to your liking.
At he end, finish sprinkling with the chopped hazelnuts ^ _ ^